For what it's worth, here's how I do it: I have my follow button that I use to keep everyone following the leader. The macro on that is:

Code:
target Leader 
focus 
follow 
target @focustarget
This keeps the focus set on the leader. That way, when I want to interact, I target the NPC with the leader and fire off:

Code:
target @focustarget 
interact
I never have any problems needing a delay between the target command and the interact command. As long as the leader is the focus (which it always is because I never change it), I can just hit the interact macro and it works.